1. Field of the Invention
This invention relates to a hydraulic pressure control device of the type having a double piping arrangement.
2. Description of the Prior Art
Heretofore, there have been provided various kinds of double channel type hydraulic pressure control devices in which a hydraulic brake system for a vehicle is divided into two channels arranged in an X-shaped configuration relative to the front and rear wheels of the vehicle and, under such a condition, braking forces on the front and rear wheels are made suitable for friction between the road surface and these wheels by having smaller forces exerted on the rear wheels than the front wheels.
In the conventionally known device of this type, the hydraulic control over one of the two channels performed by a proportioning valve mechanism disposed in that channel is arranged to be transmitted to the other channel through a balance piston so that hydraulic pressure control over the latter channel is performed in association with the hydraulic pressure control performed for the former.
The present invention is directed to an improvement on the conventional device to obtain a better balanced state of the hydraulic pressure of the channels, because in the conventional device of this type, differential pressure between the output hydraulic pressure of one channel (hereinafter called channel A) which corresponds to hydraulic brake pressure on the rear wheel and that of the other channel (hereinafter called channel B) which corresponds to hydraulic brake pressure on the front wheels moves the balance piston in the axial direction thereof to close, for example, a ball valve employed as flow passage opening-and-closing valve mechanism of the channel B; and, after that, a passage which allows the input and output hydraulic chambers of the channel B to communicate with each other is arranged to be opened and closed in relation to the rise of the output hydraulic pressure on the side of the channel A. The ball valve, which opens or closes the passage allowing the input and output hydraulic chambers of the channel B to communicate with each other, is arranged to receive, at a part which corresponds to the sectional area of the above stated communication passage, a force that corresponds to a difference between the input hydraulic pressure and the output hydraulic pressure of the channel B. This force is proportional to the increase of the differential pressure between the input hydraulic pressure and the output hydraulic pressure. Therefore, this arrangement tends to cause an unbalance between the output hydraulic pressure of the channel A and that of the channel B.